Forecasting meteorological drought through SPEI with SARIMA model

A reservoir is one of the water resource utilizations that functions as storage and provider of water, both as raw material for clean water and irrigation. Gondang Reservoir in Lamongan Regency Indonesia is a reservoir that provides water supply to 7 field reservoirs for 10 months covering an area of 6,233 ha, especially during the dry season. The Corong watershed is a watershed that flows through the Gondang reservoir. If there is a water deficit due to drought in the Corong watershed, the impact will be large for the Gondang irrigation area. Therefore, it is necessary to monitor drought in the Corong watershed. This study aimed to model and forecast the meteorological drought, represented by the Standardized Precipitation Evapotranspiration Index (SPEI) using Seasonal Autoregressive Integrated Moving Average (SARIMA). Forecasting error was evaluated using Mean Square Error (MSE). The intensity, frequency, and trend of droughts were analyzed using SPEI with a time range of 1-,3-,6-, and 12 using Rstudio. The results of the worst drought index were analyzed using the SPEI method in the 1-month worst drought in August 2003, the 3-month deficit period in February 2007, the 6-month deficit period in March 2007, and the 12-month in March 2007. The SARIMA Model (3,0,0) (2,1,0) 48 was convenient to be used for forecasting Drought index SPEI-1 in the Corong river basin area because the estimation of each of the parameters was significantly different from zero, fulfilling the diagnostic test in which the residuals from the model were random and normally distributed, and had mean squared value of 1,052. The result showed that meteorological drought was related to hydrological drought and had the potential to be affected by drought. Thus, droughts need to be prioritized in disaster mitigation.